According to the invention, the inner knurl (10) is produced by rolling a straight knurling tool (11) over the inner surface of the receiving bore (6).

A composite assembly knurling tool for forming uniformly-spaced horizontal serrations continuous across the surface of a metal flake producing drum.

The knurling tool comprises an alternating array of spacer (15, 17, 19, 21, 23) and forming discs (16, 18, 20, 22) substantially conforming to the contour of the metal flake producing drum.